Researchers have found the Sharkbot Android malware hiding under the guise of antivirus solutions on Google’s Play Store. Google recently took down at least six fake antivirus apps from the store. Attackers used these malicious apps to spread Sharkbot malware, according to a recent report. By the time the store deleted the infected apps, people had downloaded them about 15,000 times.

What is Sharkbot?

The Sharkbot malware’s main function is to steal credentials and banking information. The malware also has special features that make it dangerous. Sharkbot lures victims to enter their credentials in app screens that appear to be honest credential input forms. After a user enters their credentials, the compromised data goes to an attacker’s server.

The names of the apps Google removed from its Play Store include:

• Atom Clean-Booster, Antivirus
• Antivirus, Super Cleaner
• Alpha Antivirus Cleaner
• Powerful Cleaner Antivirus
• Center Security – Antivirus (2 versions).

These six apps came from three developer accounts, Zbynek Adamcik, Adelmio Pagnotto and Bingo Like Inc.

Sharkbot’s special tactics

According to researchers, Sharkbot stands out among Android malware due to its special features. For example, the geofencing function allows Sharkbot to ignore users from China, India, Romania, Russia, Ukraine or Belarus. Special evasion methods are also part of Sharkbot’s toolbox. If the malware detects it is running in a sandbox, it stops the execution and quits.

Sharkbot implements a highly effective toolkit for bank data theft. It hijacks Accessibility Service, which provides the app with access to all data the user sees. The malware also allows the app to interact with an interface as though it were a person.

Overall, Sharkbot runs 22 malicious commands, including:

• Request permission for sending SMS messages
• Collect and send the device’s contact list to a server
• Disable battery optimization so malware can run in the background
• Send push messages
• Imitate the user’s swipe over the screen.

Rare android malware features

Another unique feature in the Sharkbot arsenal is the use of the Domain Generation Algorithm (DGA). DGA is rarely seen in Android malware. Domain generation algorithms are malware algorithms that produce a large number of domain names. The attacker can then use the domain names as contact points with malware command and control servers. The large number makes it difficult to effectively shut down botnets. Infected devices attempt to contact some of these domain names periodically to receive updates or commands.

According to the report, with DGA one sample with a hardcoded seed generates seven domains per week, and the researchers observed a total of 56 domains per week.

During the research, 27 versions of Sharkbot were identified. The main differences between the versions were different DGA seeds and variations in botnetID and ownerID fields. The recent Sharkbot takedown is another episode in the ongoing fight against infected applications.